1. Field of the Invention
The invention relates to water-soluble organotin catalysts.
2. Description of the Prior Art
The use of organotin compounds as catalysts for esterification and transesterification reactions and for preparing or curing polymers, especially polyurethanes, polysiloxanes and polyesters, is known.
Examples of organotin catalysts common on the market are mono- and dialkyltin compounds of tetravalent tin, of the formulae:
RaSnXa3, Ra2SnXa2, [Ra2SnO]x, RaSNOOH
or 
where
Ra=alkyl group of 1 to 8 carbon atoms,
Rb=Ra or Xa,
Xa=xe2x80x94Oxe2x80x94, xe2x80x94OH, xe2x80x94Oxe2x80x94, halide, xe2x80x94ORd, OOCRd, xe2x80x94SRd, where Rd is a linear or branched, saturated or unsaturated, unsubstituted or substituted alkyl group,
x is xe2x89xa72, and y is xe2x89xa71.
The precise structure of the organotin oxides is unknown, it being assumed, however, that they are present at least as dimers.
Their use for conducting addition polymerization, polyaddition, polycondensation or curing frequently takes place in aqueous or water containing systems, in connection, for example, with the production of coatings, water-blown polymer foams, etc.
When used in aqueous or water-containing systems, organotin catalysts according to the prior art have the disadvantages of lack of solubility in water and/or lack of stability to hydrolysis and/or lack of catalytic activity.
The great majority of the known organotin compounds are insoluble or only sparingly soluble in water. If used as catalysts in aqueous systems, therefore, they cannot be used as homogeneous solutions in water but must be incorporated heterogeneously as mixtures, emulsions or suspensions, in some cases with the assistance of solvents, detergents or other auxiliaries.
Only a few organotin compounds of good solubility in water are known. Primarily these comprise highly acidic monoalkyltin and dialkyltin compounds having short-chain alkyl groups, examples being (C4H9)SnCl3, (CH3)2SnCl2, (CH3)2Sn(O3SCH3)2, and (C4H9)2Sn(O3SCH3)2.
When such organotin compounds are dissolved in water, an at least partial hydrolysis takes place immediately; stannoxanesxe2x80x94which are initially soluble in the acidic systemxe2x80x94and the corresponding acids (e.g., HCl, HO3SCH3) are formed. The acidic solutions which form are highly corrosive, which is disadvantageous for the majority of applications. Furthermore, the acids which are released reduce the catalytic activity of the organotin compounds, rendering such solutions unsuited to many catalytic applications (the condensation of silicones, for example).
If it is attempted to neutralize such acidic solutions, the organotin compounds are precipitated as stannoxanes, polystannoxanes or organotin oxides.
Organotin carboxylates and organotin alkoxides are generally neither soluble in water nor stable to hydrolysis. On contact with water, they decompose with the formation and precipitation of stannoxanes, polystannoxanes or organotin oxides.
Organotin mercaptides are generally likewise insoluble in water. Compared with other organotin compounds, however, they are notable for their greater stability to hydrolysis. However, the stability goes hand in hand with a markedly reduced catalytic reactivity.
While in certain systems (in a mixture with isocyanates, for example) a subsequent chemical or thermal activation of organotin mercaptides can take place, with the formation of more active catalysts, the catalytic activity of these mercaptides in less reactive systems, such as silicones, is inadequate, if indeed it is present at all.
There is thus a need to find organotin catalysts which are intended for use in aqueous or water-containing systems and which are storage-stable and soluble in water, contain no free strong acids, possess catalytic activity, and do not lose this activity even on prolonged storage in or contact with water.
The invention is directed to a process for preparing water-soluble organotin catalysts by contacting organotin compounds of a select formula with polyelectrolytes and, if appropriate, subsequent removal of water.
The process of the present invention is achieved by contacting organotin compounds having the general formula I
RnSnX4xe2x88x92nxe2x80x83xe2x80x83(I)
in which
R=C1-C4 alkyl, preferably CH3 or C4H9 
n=1 or 2,
X=anionic radical xe2x80x94Oxe2x80x94, xe2x80x94OH, F, Br, I, Cl preferred, xe2x80x94OR1, xe2x80x94SR1, xe2x80x94OOCR1, xe2x80x94SO3R1, preferably an anion of a strong acid, with particular preference for Cl or SO3R1, where
R1=unsubstituted or substituted alkyl, aryl or aralkyl and R, X and R1 can each be identical or different, with polyelectrolytes, especially polymers or copolymers of the general formula(e) II and/or III 
xe2x80x83in which
Y=H or CH3 
A=xe2x80x94COOZ, xe2x80x94SO3Z, xe2x80x94OSO3Z or xe2x80x94PO3Z2 
Bio=the radical of a biopolymer,
Z=H, an unsubstituted or substituted alkyl group or a cationic radical selected from the group consisting of alkali metal salts, alkaline earth metal salts or ammonium salts, preferably Z is H, CH3, Na, K, Ca or NR2R3R4R5 where R2 to R5=H or a substituted or unsubstituted alkyl group of 1-10 carbon atoms, preferably CH3, hydroxyethyl or hydroxyisopropyl, B=the radical of an ethylenically unsaturated monomer such as, for example, ethylene, propylene, butadiene, isoprene, vinyl chloride, vinylidene chloride or vinylidene fluoride, styrene, indene, vinyl acetate, vinyl alcohol, vinylformal, acrolein, methyl vinyl ketone, vinylpyrrolidone, maleic anhydride, acrylonitrile, vinyl ethers, (meth)acrylic acid, (meth)acrylamide, (meth)acrylic esters, cyanoacrylic esters, and the like; and Y, A, Z and B within k, 1 and m can each be identical or different, m being xe2x89xa70, 1 and k=0-200, especially 50-150, preferably 60-100, where 1+Kxe2x89xa720, the ratio of (1+K)/m being chosen such that the polymers in the dissociated form are soluble in water.
The polyelectrolytes which are used in accordance with the invention can comprise both biopolymers such as algic acid, gum-arabic, nucleic acids, pectins, proteins and the like, and chemically modified biopolymers such as carboxylmethylcellulose, ligninsulfonates and, in particular, synthetic polymers such as, for example, poly(meth)acrylic acid, polyvinylsulfonic acid, polyvinylphosphoric acid (vinylphosphonic acid polymers), polymaleic acid and copolymers thereof with one another and with unsaturated olefins such as, for example, ethylene, propylene, butadiene, isoprene, vinyl chloride, vinylidene chloride or vinylidene fluoride, styrene, indene, vinyl acetate, vinyl alcohol, vinylformal, acrolein, methyl vinyl ketone, vinylpyrrolidone, maleic anhydride, acrylonitrile, vinyl ethers, (meth)acrylamide, and cyanoacrylic esters.
In accordance with the invention it is possible to use all polyelectrolytes whose proportion of dissociable groupsxe2x80x94which can be a constituent or substituent of the polymer chainxe2x80x94is sufficiently great that the polymers in the dissocited form are soluble in water.
In accordance with the invention, the polyelectrolytes used are preferably the so-called polyacids. On dissociation, these give off protons to form polyanions, which can be both inorganic and organic polymers. Examples of polyacids, whose salts are referred to as polysalts, having the groups I-V as characteristic base units are: poly(meth)acrylic acid (I), polyvinylsulfuric acid (II), polyvinylsulfonic acid (III), polyvinylphosphonic acid (IV), and polymaleic acid (V): 
In addition to the base units having dissociable groups, it is also possible to use ethylenically unsaturated monomers such as, for example, ethylene, propylene, butadiene, isoprene, vinyl chloride, vinylidene chloride or vinylidene fluoride, styrene, indene, vinyl acetate, vinyl alcohol, vinylformal, acrolein, methyl vinyl ketone, vinylpyrrolidone, maleic anhydride, acrylonitrile, vinyl ethers, (meth)acrylic acid, (meth)acrylamide, (meth)acrylic esters, cyanoacrylic esters, and the like.
The proportion of these monomers, also ethylenically unsaturated, in the polymer can be adjusted according to the particular desired end properties of the catalyst, in respect, inter alia, of the fields of use. The distribution of the individual monomers in the polymer molecule can be random, or it is possible to polymerize blocks of individual monomers, with one another or among one another.
The sole condition is that the proportion of dissociable groups in the polymer is sufficiently great to keep both the polymer itself and the mixture, or the reaction product of compounds of the general formula (I) with the polyelectrolytes of the general formula (II), soluble in water.
Both the basic units and the processes for preparing the corresponding homopolymers and copolymers are part of the known prior art (compare CD Rxc3x6mpp, Chemie Lexikon-Version 1.0, Stuttgart/New York). Organotin compounds of the general formula (I) which can be used in accordance with the invention are monomethyltin, monobutyltin, dimethyltin and dibutyltin oxides, hydroxides, alkoxides, halides, mercaptides, carboxylates and sulfonates, preferably MeSnCl3, Me2SnCl2, BuSnCl3, MeSn(O3SCH3)3, Me2Sn(O3SCH3)2, BuSn(O3SCH3)3 or Bu2Sn(O3SCH3)2.
The contacting or reaction can be performed, if appropriate, advantageously in aqueous solution. A preferred procedure in accordance with the invention is to carry out dropwise addition, at room temperature and with intimate mixing, of an aqueous solution of the tin compound of the general formula (I) to an aqueous solution of the polyelectrolyte, this solution being introduced into a vessel as initial charge. The rate of addition is such that the solution in said vessel remains continuously clear. At an increased rate of addition, however, it is possible to carry out subsequent stirring until the solution in said vessel becomes clear. The amount of compounds of the general formula I is chosen such that, on the one hand, the amount of Sn present is sufficient for the intended purpose and such that, on the other hand, the catalyst still remains soluble in water. Optimization can also be undertaken by means of simple preliminary tests.
Results which are positive in accordance with the invention are generally obtained if organotin compounds of the general formula I are used in a molar ratio of 0.01-0.8, in particular 0.1-0.5, based on the groups Z of the polyelecrolytes of the general formula (e) II and/or II.
The catalyst solution prepared in this way can be used directly without further treatment stages, or stored. Alternatively, it can also be dewatered and dried by means of the known techniques and stored and used in water-free form.